A. Field of the Invention
The present invention relates to methods of reducing emissions of gaseous carbon oxides from the combustion and/or oxidation of hydrocarbons. More specifically, the present invention relates to methods for the preferential production of carbon suboxides from the combustion and/or oxidation of hydrocarbons and to uses for the produced carbon suboxides.
B. Description of the Prior Art
When hydrocarbons, such as oil, gasoline, coal and other fossil fuels, as well as renewable hydrocarbon sources such as wood, are oxidized to produce energy, a variety of different carbon-containing products are formed. The two most common carbon-containing products are carbon monoxide, CO, and carbon dioxide, CO2. In addition, some combustion and/or oxidation processes may form carbon suboxide, C3O2.
Carbon monoxide is produced, for example, when graphite (one of the naturally occurring forms of elemental carbon) is heated or burned in the presence of a limited amount of oxygen. The reaction of steam with red-hot coke also produces carbon monoxide along with hydrogen gas (H2). Coke is the impure carbon residue resulting from the burning of coal. This mixture of CO and H2 is called water gas or syn-gas and is used as an industrial fuel or feedstock for organic synthesis. In the laboratory, carbon monoxide is prepared by heating formic acid, HCOOH, or oxalic acid, H2C2O4, with concentrated sulfuric acid, H2SO4. The sulfuric acid removes and absorbs water (H2O) from the formic or oxalic acid. Because carbon monoxide burns readily in oxygen to produce carbon dioxide, as exemplified in the following reaction,2CO+O2→2CO2,carbon monoxide is useful as a gaseous fuel. Carbon monoxide is also useful as a metallurgical reducing agent because at high temperatures it reduces many metal oxides to the corresponding elemental metal. For example, copper (II) oxide, CuO, and iron (III) oxide, Fe2O3, can be reduced to the corresponding metals by carbon monoxide.
Carbon monoxide is an extremely dangerous poison as it is an odorless and tasteless gas, giving no warning of its presence. Carbon monoxide has an affinity for hemoglobin that is two hundred times greater than that of oxygen. Thus, carbon monoxide readily replaces oxygen and binds to the hemoglobin in blood to form carboxyhemoglobin that is so stable that it cannot be broken down by body processes. The ability of red cells to carry oxygen is destroyed by exposure to carbon monoxide, and suffocation may occur.
Carbon dioxide is produced when any form of carbon or almost any carbon compound is burned in the presence of an excess of oxygen. Many metal carbonates also liberate CO2 when they are heated. For example, calcium carbonate (CaCO3) produces carbon dioxide and calcium oxide (CaO).CaCO3+heat→CO2+CaO
The fermentation of glucose during the preparation of ethanol produces large quantities of CO2 as a by-product. The same process also makes breads rise.C6H12O6→2C2H5OH+2CO2
In the laboratory CO2 can be prepared by adding a metal carbonate to an aqueous acid; as illustrated in the following reaction.CaCO3+2H3O+→Ca2++3H2O+CO2
The Earth's atmosphere contains approximately 0.04 percent carbon dioxide by volume and serves as a huge reservoir of this compound. The carbon dioxide content of the atmosphere has significantly increased in the last several years largely because of the burning of fossil fuels. A so-called greenhouse effect results from increased carbon dioxide and water vapor in the atmosphere. These gases allow visible light from the sun to penetrate to the Earth's surface, where it is absorbed and reradiated as infrared radiation. This longer-wavelength radiation is absorbed by the carbon dioxide and water and cannot escape back into space. There is increasing concern that the resulting increased heat in the atmosphere could cause the Earth's average temperature to increase 2° to 3° C. over a period of time. This change would have a serious impact on the environment, affecting climate, ocean levels, and agriculture.
Carbon suboxide, C3O2, is a foul-smelling, lachrymatory gas that can be produced by the dehydration of malonic acid, CH2(COOH)2, with P4O10 in a vacuum at 140° to 150° C. Carbon suboxide is a linear, symmetrical molecule whose structure can be represented as O═C═C═C═O. At 25° C. the compound is unstable and polymerizes to highly-colored solid products, but it is a stable molecule at −78° C. Polymerized carbon suboxide (PCS) is generally considered to be a substance with variable composition as the carbon to oxygen ratio in the PCS is not constant.
Under the influence of ultraviolet light (in the process known as photolysis), C3O2 decomposes to the very reactive molecule ketene, C2O. Since carbon suboxide is the acid anhydride of malonic acid, it reacts slowly with water to produce malonic acid.
A method to use only the hydrogen component from all hydrocarbon fuels and keep carbon as a solid waste or raw material was proposed by Meyer Steinberg from Brookhaven National Laboratory [M. Steinberg, “Decarbonization and Sequestration for Mitigating Global Warming”, International Symposium “Deep See & CO2 2000”, Feb. 1-2, 2000 at SRI, Mitaka, Tokyo, p. 4-2-1-4-2-6 (http://www.nmri.go.jp/co2/4-2.pdf)]. The major drawback of this method is that only a small portion of the available hydrocarbon chemical energy is actually utilized. For example, in the best scenario for this method, only about a half of the available energy from the reactions in equations (1) and (2) is actually released and utilizedCH4→C+2H2  (1)2H2+O2→2H2O  (2)as compared to the energy produced from a complete methane oxidation, shown in equation (3).CH4+2O2→CO2+2H2O  (3)
Suboxide polymers have chemically and thermodynamically stable structures similar to humic acids, the organic component of most fertile soils, and can be used as a soil conditioner. Use of biomass as fuel is a commonly accepted way to reduce net carbon emissions, however, recent sources indicate that agricultural land use may release carbon stored in soil, effectively counteracting advantages of biomass-derived fuel. Recycling of suboxide polymer to agricultural soils can mitigate carbon losses in soil due to agriculture as well as capture the economic advantage of carbon sequestration (currently over $80 per ton of carbon).
Due to the potential environmental impact of carbon dioxide emissions, there remains a need to reduce the carbon dioxide emissions while increasing the use of energy released from hydrocarbon fuels. Production of different carbon products in the form of a solid would reduce carbon oxide production thus reducing atmospheric pollution as well as slowing if not stopping the effects of greenhouse gases on the earth.